1. Field of the Invention
The present invention generally relates to a single lens reflex camera a and more particularly to a movable mirror arrangement for use in a single lens reflex camera, the arrangement including a main mirror, at least a part there of constituting of light transmitting portion, and an auxiliary mirror.
2. Description of the Prior Art
A conventional-type movable mirror arrangement is generally constructed as follows. In finder observation state, light transmitted through a photographic lens is divided by the main mirror into a first portion of light which is reflected toward a view finder system and a second portion of light which is transmitted through the main mirror and is led by reflection on and auxiliary mirror to a photoelectric means for exposure control, focus detection, etc. In a photographing state, both the main mirror and the auxiliary mirror are retracted out of the region where light transmitted through the photographic lens passes through the camera toward a film positioned to be exposed.
Conventionally, in a single lens reflex camera provided with a movable mirror arrangement of the above-described type, it has been so arranged that as shown in FIG. 1 when, in a finder observation state, light transmitted through a photographic lens 2 is divided into a first portion and a second portion by a main mirror 4 having a rectangular configuration and suitably inclined as shown. Namely, the first portion, i.e., the light reflected by the main mirror 4, is led to a view finder system comprising a reticle or focusing screen 6, a pentagonal prism 8 and an ocular or eyepiece 10, while the second portion, i.e., the light transmitted through the main mirror 4, is reflected by a rectangular auxiliary mirror 12 disposed behind the main mirror 4 substantially at right angles with respect to the main mirror 4 so as to be led to a photoelectric means 14 for exposure control, focus detection, etc. Furthermore, it is so arranged that, in the photographing state, both of the main mirror 4 and auxiliary mirror 12 are retracted into positions as shown in broken lines in FIG. 1 so as to permit light to proceed from the photographic lens 2 to the film 5 without obstruction by the mirrors and to prevent light entering the camera through the view finder system from proceeding into the light path region between the photographic lens 2 and the photographic film 5.
Namely, when the movable mirror arrangement is moved from the finder observation state to the photographing state, the main mirror 4 is pushed upwardly in the direction indicated by arrow A in FIG. 1 and, at the same time, the auxiliary mirror 12 is pivoted towards the main mirror 4 in the direction indicated by arrow B in FIG. 1 so as to be overlapped on the main mirror 4 in a parallel relation therewith as shown in broken lines in FIG. 1.
A mirror operating mechanism as referred to above is disclosed, for example, in U.S. Pat. No. 4,293,209 wherein the main mirror is caused to swing from the view finder observation position to the photographing retraction position wherein the auxiliary mirror introduces light passed through the main mirror when positioned in the finder observation position to a light-measuring element. In the above described U.S. Patent, the auxiliary mirror is mounted swingably on the main mirror and has a rotary shaft around which the auxiliary mirror can swing. Further, it is so arranged that both ends of the rotary shaft are rotatably mounted on both sides of a frame supporting the main mirror and the end portion of an operating arm of the auxiliary mirror is brought into contact with a cam fixedly secured to a stationary member by means of a spring. More specifically, referring back to FIG. 1, the main mirror 4 has a light-dividing portion in the center thereof for dividing incident light into the two portions as described above through reflection and transmission thereof. More specifically, it is so arranged that, in the photographing state, the light-dividing portion is covered by the auxiliary mirror 12 and an auxiliary mirror holder (not shown) for holding the auxiliary mirror 12 so as to prevent light from proceeding through the view finder system and into the optical path region between the photographic lens 2 and the film 5, because such light is detrimental to photographing.
However, it should be noted here that since, as a matter of fact, a main mirror holder for holding the main mirror 4 and and auxiliary mirror holder for holding the auxiliary mirror 12 are also provided in the above-described arrangement shown in FIG. 1, it may undesirably occur that the auxiliary mirror holder is left in the optical path region described above in the photographing state without being displaced to the position shown in broken lines in FIG. 1 due to such a complicated structure.
In order to eliminate such a phenomenon, it may be so arranged that the main mirror holder is formed with a rectangular opening for accommodating the rectangular auxiliary mirror 12 therein so that a part of the auxiliary mirror 12 may be fitted into the rectangular opening in the photographing state. However, in such an arrangement since the rectangular opening should be formed larger in size than the auxiliary mirror such that the auxiliary mirror may be loosely fitted into the rectangular opening, four clearances are undesirably formed between four side edges of the rectangular opening and corresponding four side edges of the rectangular auxiliary mirror 12. If such clearances are incompletely shielded against light in the photographing state, light incident reversely from the view finder system proceeds through the clearances into the optical path region between the photographic lens to and film, which is detrimental to fine photography.